Resistance to stress corrosion cracking of new Al-Mg-Cu alloy containing Sc

In 3.5% NaCl solution, the stress corrosion cracking properties of a new Al-Mg-Cu alloy containing scandium were examined. The composition and the micro-morphology of the crack tip were analyzed. According to the linear elastic fracture mechanics, the stress field on the crack tip of the pre-fatigue crack specimen is in a state of plane strain. The crack propagation rate as a constant speed, the stress intensity factor on the crack tip and the threshold stress intensity factor for the stress corrosion cracking are obtained. The results of the scanning electron microscopy and the EDS analyses indicate that the intergranular cracking is dominant in the stress corrosion cracking, due to the fact that the Al₂O₃ is formed with the oxygen dissolved in the corrosion medium around the pre-crack. Anodic dissolution reaction occurs for the matrix around the crack tip, and the corrosion products are mainly aluminum chloride.